The presence of a cardiovascular complication in a patient entails an important health risk, which forms one of the leading causes of morbidity and mortality in Europe and North America. A reliable diagnosis of such a cardiovascular complication has a significant impact on successful treatment, which is particularly important for patients showing symptoms of acute coronary syndrome (ACS), since such symptoms of ACS imply a heightened risk of experiencing irreversible cardiac injury. An acute coronary syndrome is caused by a blockage in a coronary artery which substantially cuts off the blood supply to connected areas of the myocardium, resulting in acute myocardial ischemia.
Patients with chest pain or signs of instable angina or ACS may frequently present to their doctor or to the emergency room for clinical evaluation, which includes evaluation of their medical history specifically directed to evidence of existing cardiovascular disease or risk factors therefor, analysis of the type of symptoms as described, as well as clinical signs associated with acute coronary syndrome such as evidence of pulmonary edema, hypotension, tachycardia or bradycardia. Furthermore, an electrocardiogram (ECG) and laboratory tests may be performed. From the evidence obtained, a diagnosis may be established which includes confirmation of the suspected ACS and a differential diagnosis for, for example, unstable angina pectoris (UAP), ST-segment elevation myocardial infarction (STEMI) or non-ST-segment elevation myocardial infarction (NSTEMI). Particularly, the ECG may provide important information for confirmation of ACS and differential diagnosis. The interpretation of ECG signals is known in the art. Particularly, if the ECG shows elevated ST segments, a ST segment elevated myocardial infarction (STEMI) is diagnosed.
Myocardial infarction (MI), also termed heart attack, is known as cell necrosis in the myocardium resulting from ischemia. Myocardial infarction can be caused by the sudden occlusion or significant narrowing of a coronary artery. The sudden narrowing or occlusion of a coronary artery is frequently caused by the formation of a thrombus after plaque disruption. In case of insufficient collaterals, blood flow is obstructed and the affected myocardium becomes ischemic.
It is well established that the duration of coronary artery occlusion is significant to the nature and extent of myocardial damage. In a first stage after artery occlusion, ischemic damage occurs. This damage may be fully reversible if sufficient blood flow of the occluded artery is reestablished within a short period in time. However, If reperfusion is only achieved within 2 to 4 hours after ischemia, irreversible cardiac injury will develop and postischemic dysfunction may furthermore develop in other parts of the myocardium. Thus early intervention is needed to save myocardium by protecting the affected myocardium from necrosis and to prevent late sequelae of necrosis such as heart failure and to reduce long-term and short-term mortality.
Delayed medical attendance may therefore be an important risk to the health of patients with ST elevation myocardial infarction (STEMI). A substantial patient delay, e.g. defined as the time from symptom onset until first medical contact, can form a leading cause of death in patients with STEMI. In developed countries, median delay time from symptom onset to hospital arrival may range from 1.5 hours to more than 6 hours. Observational studies from data registries indicate that 1 hour reduction in delay may be associated with more than ten extra lives saved per 1000 patients treated. The potential benefits of reducing patient delay may even be underestimated as patients with STEMI dying from ventricular fibrillation in the pre-hospital phase are often not included in registry studies.
Furthermore, the effect of education and public information campaigns on the decision of patients to seek early medical attendance appears rather limited. Therefore, methods for self-diagnosis and early detection of acute coronary artery occlusion (CAO), e.g. a method which allows the subject to perform an initial risk assessment for CAO and/or for establishing a probability of occurrence of a STEMI event, may form an important tool for motivating patients to seek medical assistance in elevated risk situations, and may thus improve the efficiency of medical emergency services, e.g. by reducing the inflow of false positive cases and improving the inflow of patients having an early recognized risk of suffering a STEMI.
Electrocardiograph (ECG) devices for recording bioelectric data from a body are known in the art. For example, in U.S. Pat. No. 6,055,448, a device is disclosed which comprises an array of electrode leads for detecting an electrical signal associated with components of a heartbeat. In a known configuration, such a device can be embodied in an electrode vest comprising, for example, 80 electrode leads. However, for devices and method for self-diagnosis and early detection of acute coronary artery occlusion (CAO), e.g. for performing an initial risk assessment, simple means for recording, e.g. requiring only few electrode leads and simple yet robust means for ECG analysis are preferred.
In U.S. Patent Application No. US 2005/0085736, a portable ECG detector device is disclosed for detecting a myocardial infarction. The device includes a processor which records a baseline ECG from a plurality of electrodes. If data representing current bodily activity deviate from the baseline ECG by a predetermined deviation value, the user is notified to seek medical attention. The baseline ECG reference data thereby typically is recorded for a user lying down in a supine position having his legs raised. While this prior art device allows detection of elevation or depression of the ST-segment above or below a predetermined level in relation to the baseline ST-segment recording, there is still room for improved sensitivity and specificity for raising an attention signal, for example, to avoid that normal physiological variations are mistaken for a ST-segment deviation indicative of a health risk.